Sometimes the ObjectDB throws an internal exception if a find() was executed. It is a sporadic issue that occurs only with Objectdb 2.7.0_b2 and only if the entites are enhanced. (We don't enabled the new property "objectdb.temp.extended-ref-retrieval" from http://www.objectdb.com/database/forum

the iteration can be avoided and complex queries over millions of objects can be executed quickly ... execution. Indexes are especially efficient in lookup and range queries: SELECT p FROM Point p WHERE p.x ... enables quick execution of the following queries: SELECT p FROM Point p WHERE p.x = 100 AND p.y = 100

with a PersistenceManager. Multiple queries might be executed simultaneously by different threads, but the implementation might choose to execute them serially. In either case, the implementation must be thread safe ... : this.fieldName. The Query interface provides methods which execute the query based on the parameters

the database, DELETE queries do not retrieve data from the database, but when executed, delete specified ... queries can only be executed within an active transaction and the changes are visible to other users ... all the objects in the database:
DELETE FROM Object DELETE queries are executed using the executeUpdate